A SQUID is a sensor for measurement of magnetic flux. A SQUID is coupled with a flux transformer in the performance of measurement of a magnetic field, the flux transformer converting the magnetic field into a flux. A conventional flux transformer is comprised of a so-called pick-up coil for field-flux conversion and a coupling coil for further conduction of the flux to the SQUID. Such a construction is referred to as a SQUID magnetometer. A measure of the functional capability of a SQUID magnetometer is the field sensitivity. To operate a rf-SQUID-magnetometer, the latter is generally coupled to an electric resonant circuit, also called a tank circuit, into which a high-frequency current is fed at the resonance frequency of the tank circuit. The SQUID damps the tank circuit with a degree of damping dependent upon the magnetic flux through the superconductive ring. As a result there is a change in the voltage drop across the tank circuit which is used as a read-out for the SQUID.
From EP 04 18 848 A2, a LT.sub.c -RF-SQUID with an integrated microwave resonator is known. In this case the superconductive ring as well as the tank circuit are formed in one component. The tank circuit is comprised of a strip conductor. The electrical length of the strip conductor corresponds to a half microwave .lambda. of the operating frequency and thus forms a .lambda./2 microwave resonator. The strip resonator is capacitatively connected to the evaluation electronics.
To reliably set the resonator characteristics, the SQUID is arranged symmetrically relative to the strip conductor. This symmetry further allows the SQUID to be at a location of maximum current flux which ensures a sufficiently good coupling between resonator and SQUID. One such construction is fabricated from high temperature superconductive materials in accordance with Appl. Phys. Lett. 60(18), p. 2303, 1992.